1. Field of the Invention
This invention relates to an industrial truck, particularly a high-lift truck, also as a high-lift truck having a displaceable mast.
The invention relates generally to an industrial truck and particularly to a high-lift truck, which truck comprises a lifting frame, particularly a frame comprising extensible mast sections and at least one vertically movable load-carrying carriage, wherein the fixed mast section and any extensible mast section are provided each with laterally disposed, vertical rails, which serve in alternation as carriers for rotatably mounted guide rollers for engaging guideways of adjacent rails or as guideways for such guide rollers, wherein guide rollers are provided on the load-carrying carriage and particularly at the top end of a lower or outer mast portion or of an extensible mast section, and at the bottom end of an inner extensible mast section, and the guideways are provided at least on one side with a bordering ledge for laterally guiding the guide rollers.
The term "industrial truck" and "high-lift truck" include high-lift trucks having a displaceable mast and provided with laterally disposed, inwardly open guide rails for a lifting frame carrier, which carries guide rollers running in the guide rails.
The invention covers also industrial high-lift trucks having a displaceable mast and inwardly open horizontal guide rails for guiding guide rollers which are axially fixed in bearings on the lifting frame.
The invention is also applicable to vehicles having an inclinable mast.
In such vehicles, the mast may be moved to an inclined position for transport trips so that loads will be more reliably held e.g., on fork prongs of the load-carrying carriage.
Such lifting frame may consist of a fixed or lower mast section, in which only one load-carrying carriage is guided, or with a lower or fixed mast section and extensible mast sections. The mast may consist of three or two sections.
2. Description of the Prior Art
Such lifting frames are known, e.g., from Published German Application No. 3,041,821. A problem arising in connection with such lifting frames resides in that the individual mast sections, particularly extensible mast sections, should be guided not only in forward and rearward directions but should also be laterally guided. It is known to provide rollers which are offset 90.degree. for a lateral guidance. But such rollers involve a considerable expenditure and particularly if the lateral struts of the mast sections consist of rails such rollers will require additional space. Besides, said rollers add to the weight of those mast parts which are to be moved.
Extensible mast sections have, on an average, a length of about two to three meters. This fact gives rise to problems. The side portions of the mast sections, i.e., the laterally disposed rails for the guide rollers, which are rotatably mounted in fixed positions in known manner, have previously required to be exactly aligned so that loads can uniformly be taken up by all rollers. The mast sections must be manufactured with very accurate parallelism. But tolerances of such components are inevitable so that expensive adjusting work is required and special means must be provided for such adjustments.
It will be understood that the lifting frame may be provided with drive means, such as laterally or centrally disposed cylinder-piston units, for extending vertically movable mast sections. In such arrangements it is known to provide drive chains between mast sections which are guided on each other and may consist of extensible mast sections, and said chains may be so arranged that when a vertically movable part of the lifting frame has been extended by directly acting drive means, other parts will be carried along as the extending operation of the drive means is continued, e.g., when the driven part is a load-carrying carriage and has reached its top position in the mast section in which said carriage is guided. Such extending drives are known and may be included within the scope of the invention in any known form. Attention is directed, e.g., to German Patent Specification No. 1,041,864 disclosing a three-part mast.
A particularly high expenditure will be involved in known arrangements in the maintaining of exact tolerances if guideways for guide rollers are formed by C sections, which confine the guide rollers also on their sides by bordering ledges in order to prevent a transverse canting, as is disclosed in German Patent Specification No. 1,273,422. Such a design will adversely affect the operation because the rollers may be seized. Such lifting frames are particularly unsuitable for lateral stacking operations.
From U.S. Pat. No. 2,321,029 it is also known to provide for an engagement between guide rollers and the associated guideways on profiled surfaces, e.g., by the provision of grooved surfaces on the treads of the guide rollers and of guideways provided with bordering ledges which have a mating shape in cross-section.
The term "bordering ledge" covers also laterally disposed external rails or webs which are provided at the guideways and border a guide roller on the outside in the same manner as a so-called C section.